High efficiency ion exchange system for removing arsenic from water

ABSTRACT

The disclosed invention is a fixed bed ion exchange system from removing arsenic from water. It employs a combination of electronically controlled process steps and specific systems configurations to duplicate the effects of moving resin beds from one operating position to another as is required in moving bed ion exchange water purification systems. The invention combines features of single fixed bed ion exchange systems with those of a moving bed system.

This application claim the benefit of Provisional Application No.60/243,647, filed Oct. 25, 2000.

FIELD OF THE INVENTION

This invention relates to ion exchange systems for removing arsenic fromwater. More particularly it relates to fixed bed ion exchange systemsfor removing arsenic which are configured to yield the flexibility andefficiency of moving bed systems.

BACKGROUND AND STATE OF THE ART

Ion exchange is a chemical process often used to separate certaincontaminant substances from a drinking water supply containing a mixtureof several other harmless dissolved substances. For example, commonground water used for drinking water will contain substances such as theionic forms of calcium, magnesium, sulfate, chloride and bicarbonate. Inmany cases, the water may also contain contaminants that are known to bedetrimental to health. Such ionic substances as nitrite, nitrate,arsenic, antimony, fluoride, selenate, chromate, perchlorate and othersimilar harmful substances are often found. It is desirable to separateout the contaminants harmful to health by treating the water with an ionexchange system. There is a special interest in removing arsenic to verylow levels.

Ion exchange processing systems range in production capacity from 50gallons per day (GPD), such as is used in home water softeners and waterpurification devices, to very large plants having a capacity of severalmillion gallons per day (50 to 100 million GPD) for centralizedtreatment of a public water supply.

Various equipment configurations or systems of vessels, plumbing andvalves are used to apply the ion exchange process to the above purposeof treating a water supply to remove undesirable substances. Forexample, one prior art system is shown in FIG. 1 as system 100. Thissystem is referred to as a single “fixed bed” design. The water to betreated is pumped from line 10 through a vessel 12 containing a bed 14of ion exchange resin. Purified water is removed via line 16. Note thatthe word “single” indicates that all process streams flow through thevessel 12 only once before continuing flow. Also the term “fixed bed”indicates that all ion exchange vessels are fixed in their positions.)During operation, there is no visible change in the positioning of thevessels or piping or any other component, only the internals of thevalves change as they go from open to closed. (In contrast, when amoving bed system is in operation the position of the vessels and pipingchange and a multiport valve remains in a fixed position.

The vessel 12 containing the bed 14 is equipped with about eight toeleven different valves which control which process stream passesthrough the ion exchange bed. These are large full capacity valvescapable of handling 50 to 100 percent of the peak flow rate through theplant. Practical flows of 500 to 1000 gallons per minute or morecapacity for valve passage are not uncommon. By selecting the proper setof valves to be opened or closed either manually or by electroniccontrols, the flow of water to be treated by being passed through thevessel 12 and resin bed 14 can be stopped when the resin bed isexhausted. Control valve operations allow a sequence of process steps tobe executed involving rinsing, regenerating and back washing anddeclassification (if required) to restore the adsorptive capacity of theresin. This sequence of steps produces a quantity of waste water thatcontains waste salt materials. This quantity of waste water isdiscarded. In FIG. 1 regenerant solution, such as brine, is shownsupplied via line 18 and removed via line 20 and rinse liquid is shownbeing supplied via line 22 and removed via line 24.

Use of a single fixed bed of the prior art is also similar to a batchoperation in that the flow of treated water is stopped completely whilethe resin goes through the resin regeneration steps. If an uninterruptedflow of treated water is desired, at least two fixed bed units must beused in parallel. Each bed is operated as above. After the first bed isexhausted, the bed is taken off line and regenerated while the secondbed is placed into operation.

In general, a fixed bed system is comprised of as few vessels as iseconomically possible from the cost equipment point of view. Keeping thenumber of vessels to a minimum also reduces the number of large valvesto be maintained or replaced. It also simplifies the valve controlsystem with fewer valves to operate. It is customary therefore for plantdesigners to minimize the number of vessels to keep the number of valvesto a minimum.

There are disadvantages, however, because larger vessels and largevalves are required. To maintain or replace vessels or valves on atwelve foot diameter vessel, two or three men are required with the aidof heavy equipment lifting devices. Operation and maintenance costs willrise when first equipment costs are low because of large vessels. Apopular design of a fixed bed system uses three vessels. Twenty four tothirty three large valves must be operated and maintained on such asystem.

With a fixed bed system it is also often required to declassify theresin bed after regeneration. This step requires time and process waterand produces additional waste water. The present invention eliminatesthis step.

Another prior art ion exchange system is known as a moving bed system oras a “merry-go-round” design. In this system the ion exchange resin iscontained in several small vessels containing only an inlet port and anoutlet port. Multiport valves communicate with these ports and controlwhich process stream flows through each vessel. FIG. 2 depicts such asystem as 200. These systems eliminate the use of large vessels and thesubsequent high maintenance and replacement costs. In these systemsmultiple vessels 12, such as eighteen vessels numbered 1 through 18 aremounted on a circular platform 26 near the perimeter of a platform thatslowly rotates while the system is in operation. The vessels 12 are eachcoupled through a line 32 to an upper multiport valve 28 and through aline 34 to lower multiport valve 30. Valves 28 and 30 can be combined orseparate as shown.

The multiport valves are constructed with fixed (in and out) portscorresponding in position to the (in and out) ports of the ion exchangevessels which rotate part. The types of process streams flowing throughthe various vessels is controlled by the multiport valves 26 and 28 andis dependant on the position of the vessel on the circular platform.Consequently, as the platform rotates, the process stream entering andleaving any of the vessels changes according to a predetermined anddifficult to alter process flow, set by the multiport valves.

Returning to FIG. 2, the system 200 shown therein has eighteen discreetvessels 12 and eighteen discreet positions for a vessel on the circular,rotating platform 26. The rotation of the platform physically moves eachvessel from one position to the next position with all eighteen vesselsmoving simultaneously. The multiport valves 26 and 28 are positioned inthe center of the rotating platform. The main process streams of treatedwater, regenerant, and rinse are first fed to the central multiportvalves that then select the appropriate process stream for each positioninto which a vessel can be placed.

For example, a single vessel physically moves from position to positionas shown in FIG. 2 When a given vessel is in positions 4 through 18 onthe merry-go-round, it is fed untreated water from line 10 through valve26 and line 30 which it purifies and discharge via line 32, valve 28 andline 16. As the vessel moves from position 4 through to 18 it continuesin water treatment service but at each successive step the resin becomesmore and more loaded with contaminant until it is virtually exhausted inposition 18. When the vessel is moved into positions 1 through 2, abrine stream enters the vessel via line 22, valve 28 and line 32 toregenerate the resin by displacing contaminant off of it. Spentregenerant is removed via line 34, valve 30 and line 24. When the vesselis moved into position 3, a rinse and/or backwash stream enters thevessel via line 18, valve 30 and line 34 to displace regenerantsolution. Rinse is removed via line 32, valve 28 and line 20. Aftermaking a complete rotation around the merry-go-round the vessel againenters the adsorption section starting at position 4 and advances stepby step again to repeat the cycle.

One result of this configuration is the elimination of the large singleport valves which were required for the fixed bed design. Practicaldesigns for the moving bed systems incorporate numerous small vessels asdictated by mechanical stability and weight distribution considerations.The most mechanically stable systems use several (ten to forty) smallvessels mounted on the “merry-go-round” to obtain an evenly distributedmechanical load.

These conventional systems present the following disadvantages.

High Wastewater Production

Conventional ion exchange systems are usually designed to keep equipmentcosts and operator and maintenance costs to a minimum while producing awater suitable for consumption. The generation and disposal ofwastewater produced by ion exchange systems is usually a less importantconsideration. Conventional systems will produce from two to ten percentof the plant production as wastewater. The present invention minimizeswaste water production and minimizes those operating costs dealing withthe production and disposal of waste water. In many cases, the disposalof waste is a major cost of operation and becomes most important whenoperation over several years is considered. The invention produces aslittle as ten to thirty percent of the waste produced by conventionaldesigns.

High Valve Maintenance and Spatial Requirements

Another disadvantage of the fixed bed system is the large number ofheavy and bulky automatic valves needed to control the process flowsthrough each vessel and the use of large diameter vessels. The maindisadvantage of the moving bed system is that it requires two to threetimes the space and also requires very large and complex specializedmulti port valves and a complex plumbing design. The net result is a farmore costly system—approximately three times the cost of its fixed bedcounterpart.

Mechanical Instability and Cost

Another disadvantage of the moving bed system is its inherent mechanicalinstability. It presents a high center of gravity on top of a centralmounting pivot. This design is subject to relatively small earthquakeforces. Steel girder supports are often required to enhance stability,but cost increases.

Design Inflexibility

Disadvantages common to both systems of the art in comparison to theinvention are that the process flow design for each conventional systemmust be fixed at design time. Fixed mechanical elements will determinethe process stream that enters and leaves each vessel. To alter theprocess design at run time, the valves built into the rotating platformor the multiport valve, which rotates in unison with the rotatingplatform, must be mechanically altered or completely redesigned. Runtime changes in a fixed bed system will also require physical changes tothe system such as re-plumbing a portion or all of the vessels andvalves.

The present invention allows flexibility in process design and equipmentand optimum placement of vessels and piping to maximize processefficiency and minimize wastewater production. It permits any vessel tobe out of service at any time. Other advantages are discussed below.

STATEMENT OF THE INVENTION

This invention provides a special water treatment system for removingarsenic comprised of a combination of ion exchange vessels, valves,piping and plumbing, electronic controls and processing sensors. Thissystem is more efficient to construct, maintain and operate thanconventional systems. The invention combines features of fixed bedsystems with those of moving bed systems.

The invention applies to the treatment of water having typical drinkingwater components such as calcium, magnesium, sodium and chloride ionsbut also containing arsenic and optionally other undesirable inorganiccontaminants such as nitrate, perchlorate, antimony, chromium, selenateand/or vanadium ions.

A particular advantage of the invention is its ability to providetreated water with a markedly reduced amount of waste water beingproduced.

We now have devised a fixed bed system for ion exchange removal ofarsenic from water which embodies the advantages of a moving bed systemwithout the size and cost of a moving bed design. The present designinvolves employing a substantial plurality (at least ten and preferablyfrom about ten to about twenty-five) of fixed bed vessels which do notmove but which can be accessed by the various process flows using aseries of controller-actuatable valves, for examplemicroprocessor-controlled valves. The system uses closely clustered,fixed position, multiple vessels combined with valves and piping soarranged to obtain the cost advantages of using small mass-producedvessels and valves, and a combination of easily maintained valves.

The present invention achieves (1) high process efficiency, (2) processflexibility, (3) low wastewater production, and (4) constructioncompactness and maintenance ease.

The invention uses several relatively small diameter fixed vessels eachwith two ports, one on each opposite end. These ports are closelyassociated with small volume headers. These headers are connected tomanifolds used to conduct the process fluids to and from the vessels. Anest of small, easily-accessible process control valves is mountedbetween the headers and the manifolds.

Thus, in one aspect this invention is embodied as a system forcontinuously removing arsenic and other contaminants from arseniccontaminated water. This system includes a plurality of immobilevessels, each containing a resin bed capable of binding the contaminantsfrom the contaminated water and yielding purified water and acontaminated resin bed. The vessels each have a first fluidcommunication opening (port) at a first end and a second fluidcommunication opening at a second end. The resin bed is located betweenthe two ports.

Each vessel has two headers directly adjacent to the two ports. Theseheaders are connected to the ports with a minimum of dead volume. Eachof the headers is directly connected through automatically-actuatablevalves to a series of manifolds which supply the various process feedsand accept the various process products.

The actuatable valves are controlled by a controller to flowarsenic-contaminated water from a manifold through the resin beds in afirst subset of the plurality of vessels. This causes these resin bedsto remove arsenic and other contaminants from the contaminated water anddeposit the contaminants upon the resin in the beds and yield treatedwater. This treated water is removed from these vessels to a secondmanifold. The controller sets other valves to simultaneously flowregenerant solution from a manifold through at least one resin bed in asecond subset of the plurality of vessels to regenerate its resin bedand to remove spent regenerant solution from these vessels. Thecontroller also directs other valves to flow rinse water from a manifoldthrough at least one regenerated resin bed in a third subset of theplurality of vessels to rinse its regenerated resin bed and to passspent regenerant and/or used rinse water from the vessels in this thirdsubset. The arsenic-loaded used regenerant is treated to recover arsenic

In another aspect this invention is embodied as a continuous process forpurifying arsenic containing water. This process involves the followingsteps:

Contaminated water is fed through a first manifold toindividually-valved first headers each directly adjacent to a first portof a first subset of a plurality of immobile vessels. Each of thesevessels contains a resin bed between this first port and a second port.The resin bed is capable of binding arsenic from the contaminated waterand yielding treated water and an arsenic-contaminated resin bed.

Treated water is removed through the second port from each of thevessels in the first subset, and passed through a secondindividually-valved header directly adjacent to the second port andthrough a second manifold to a treated water discharge.

Simultaneously, regenerant solution is fed to an individually-valvedheader directly adjacent to a first or second port on one or moreadditional vessels making up a second subset of the plurality. Each ofthe vessels in this second subset contains an arsenic-contaminated resinbed. The regenerant solution is passed over the contaminated resin bedso that the regenerant displaces the arsenic and other contaminants offof the contaminated resin bed to yield a regenerated resin bed and spentregenerant solution which is removed from the other port on the vesseland through another individually-valved header directly adjacent to thisport. This regenerant solution is then processed to isolate the arseniccontaminant as a solid which is collected and handled as a toxic waste.

At the same time that the first subset of vessels is removing arsenicand producing purified water, rinse water is fed to anindividually-valved header directly adjacent to a first or second porton one or more additional vessels making up a third subset of theplurality. Each of the vessels in this subset contains a resin bed thathas been treated with regenerant. The rinse water is passed over theregenerated resin bed to yield a rinsed, regenerated resin bed and usedrinse water which is removed from the other port on the vessel andthrough the individually-valved header directly adjacent to thisopening.

In preferred embodiments, the directions of flow of the water regenerantand rinse are specified and the flows of regenerant and rinse are inseries through more than one vessel.

DETAILED DESCRIPTION OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described with reference being made to theaccompanying drawings in which:

FIG. 1 is a schematic side cross-sectional view of a typical singlefixed bed ion exchange unit of the prior art;

FIG. 2 is a schematic perspective view of a typical multiple movingvessel ion exchange unit of the prior art showing representative processflows;.

FIG. 3 is a schematic top view of a multiple fixed vessel ion exchangeunit of the present invention;

FIG. 4 is a schematic side partially cross-sectional view of an ionexchange vessel and associated piping for use in the multiple vessel,fixed vessel, water purification systems of the present invention;

FIG. 5 is a schematic side cross-sectional view of an ion exchangevessel similar to that shown in FIG. 4 with a simplified piping scheme.The vessel is set up for use in the multiple vessel, fixed vessel, waterpurification systems of the present invention with cocurrent treatmentand regeneration;

FIG. 6 is a schematic side cross sectional view of an ion exchangevessel similar to that shown in FIG. 5 but set up for countercurrentregenerant flow and preferred for arsenic removal;

FIG. 7 is a schematic side elevational view of a multiple fixed vesselion exchange system 700 of the present invention showing representativeprocess flows;

FIG. 8 is a schematic view of a system 800 corresponding to the systemof FIG. 7 but adapted specifically for countercurrent regeneration andpreferred for arsenic removal;

FIG. 9 is a schematic cross-sectional view of an ion exchange vesselused in the systems of the invention showing that preferably the ionexchange resin substantially fills the vessel and illustratingrepresentative distributors for assuring a proper fluid flow through thevessel;

FIG. 10 is a detail of FIG. 9 showing fluid flow distributors;

FIG. 11 is a schematic cross-sectional view of two sets of ion exchangevessels, illustrating a regeneration scheme of the prior art and aregeneration scheme in accord with the present invention;

FIG. 12 is a graph comparing regeneration efficiency of the tworegeneration schemes illustrated in FIG. 11;

FIG. 13 is a block diagram showing the use of an ion exchange system ofthis invention in an overall process for removing arsenic from wastewater.

DESCRIPTION OF PREFERRED EMBODIMENTS

Definitions

Further explanations of the process and systems of this invention usethe following terms:

“Bed volume” refers to a volume of fluid passed through a treatmentvessel and passed over a bed of resin. A “bed volume” is the volume ofan empty vessel and thus need not take into account the volume of resinpresent in the vessels or the volume of any piping or distributorspresent within the vessel. Typically, the resin and piping fill about70% of a bed volume and the head space above the resin and the voidsbetween the resin particles make up about 30% of a bed volume.

“Directly adjacent” and “directly attached” define the relationshipbetween the ports on the ion exchange vessels and the headers associatedtherewith and set forth that the headers are positioned very close tothe ports to minimize fluid hold up volume. These terms have the samemeaning when defining the relationship between the headers and themanifolds and between vessels.

“Header” is a zone in a pipe where several other pipes come together.

“Manifold” is a pipe that conducts a process stream from its source toall of the vessels in the ion exchange system.

“Step” refers to a part of the process that is conducted within an ionexchange vessel. The overall process is defined as the sum of all thesteps of the process. Many steps may occur simultaneously in the entiregroup of working vessels, however, any given vessel progresses in anorderly manner through a sequence of steps.

Design Features

The system and method of this invention employ and embody the followingdesign features:

1. A substantial plurality of ion exchange vessels, for example fromabout ten vessels to about one hundred vessels, are used.

2. Each vessel is equipped with two fluid entry/exit ports, one oneither end of the body of resin contained within the vessel.

3. The vessels are located directly adjacent to one another to minimizehold up volume of interconnecting piping.

4. The vessels have headers directly attached to their fluid entry/exitports.

5. Manifolds are used to conduct the process fluids from a common supplyof each fluid to the headers on each vessel.

6. The headers are directly adjacent to their associated manifolds.

7. Individual valves are present in the lines directly coupling eachmanifold to each header.

8. Any process fluid can enter and flow through any vessel or selectedgroup of vessels at any time under the control of the individual valvesand an automated controller.

9. Process fluids can flow through several vessels consecutively (as inseries configuration) or simultaneously (as in parallel connection)under the control of the individual valves and the controller.

10. The vessels are filled as full as possible with resin to furtherminimize hold up volume within the vessels.

The ion exchange systems of this invention employ a substantialplurality of treatment vessels. FIG. 3 depicts one physical arrangementof the multiple vessels in the system 300 of this invention showingeighteen vessels in two rows of nine vessels each. A piping gallery ofmanifolds can be located between the two rows directly adjacent to theheaders on the vessels. A different configuration could consist of onerow of eighteen vessels, three rows of six vessels, or the like withdirectly adjacent manifold galleries. The number of vessels can varyfrom about ten to about one hundred vessels but typically from about tento about thirty vessels and particularly ten to twenty-five vessels.

The vessels are stationary and positioned directly adjacent to eachother. Fluid access to the individual vessels is controlled bycomputer-controlled individual valves between the headers and themanifolds to allow any vessel to be in any step of an ion exchangeprocess. These are generally small, single port valves.

In essence, the invention can be described as consisting of numerousfixed bed vessels closely positioned to each other and to process streammanifolds so as to minimize the process stream piping, whose processstream flows are sequentially controlled and integrated to provide avariety of process designs which are not achievable by conventionalsystems. The invention uses a cluster of small single port valveslocated between the headers and the manifolds. The invention uses aprogrammable logic controller program to regulate and sequence the flowsthrough these valves to and from the vessels. This controller opens orcloses the individual valves at each individual vessel to controlprocess streams. The operator, by re-programming the controller, canalter these portions of the process.

The relationship of the fluid flows to a typical vessel is shown assystem 400 in FIG. 4. There a vessel 12 is depicted filled with resinbed 14. Vessel 12 is equipped with two headers, 40 and 42. These headersare attached to ports located at opposite ends of vessel 12 with resinbed 14 in between them. For the sake of this description, header 40 isshown as the header through which arsenic-contaminated water is fed and42 is the header through which treated (purified) water is removed. Itwill be appreciated that while this downflow mode of operation is mostcommon it is merely representative and that an upflow or side flowconfiguration could be used if desired. Although not depicted in detailin FIG. 4 the two headers are mounted close to the two fluid accessports on vessel 12. That means that lines 44 and 46 are generally asshort as is practical. This minimizes the hold up volume in the systemand thus minimizes the amounts of excess fluids which are likely to endup in waste.

In one embodiment as shown in FIG. 4, a series of manifolds, 48, 50, 52,54 56 and 58, and optionally 59 and 60, surround vessel 12. Thesemanifolds are in valved fluid communication with headers 40 and 42.Manifold 48 distributes untreated water to all of the vessels. Untreatedwater flows through line 10 and valve 62, when open, to header 40 andthence through line 44 to vessel 12. Again, the distance from valve 62to header 40 should be as small as possible to minimize fluid hold up.Treated water is removed via line 46 to header 42 and thence thoughvalve 64, when open, and line 16 to manifold 50 for collection anddischarge as purified product water. Multiple vessels will be carryingout the same process step with their valves 62 and 64 set to allow theflow of untreated water from manifold 48 to these vessels and thecollection and discharge of treated water out through manifold 50.

When the resin bed 14 becomes contaminated with arsenic and requiresregeneration, the flow of untreated water can be halted and a regenerantsolution can be fed from manifold 52 through line 18 and valve 66 toheader 40. In one generalized mode of operation, this flow of regenerantwill push treated water out of vessel 12. This water can be passed outthrough header 42 and manifold 50. When regenerant breakthrough is aboutto occur at the base of resin bed 14, valve 64 can be closed and spentregenerant can be redirected from header 42 through valve 68 and line 20to manifold 54 for disposal. Once regeneration is complete, the flow ofregenerant from manifold 52 can be halted and rinse water, which istypically treated water, can be fed from manifold 56 through line 22 andvalve 70 to header 40. This rinse water flow can initially push outregenerant such as to manifold 54. Thereafter, the rinse water flow caneither be directed through valve 68 to manifold 54 or be routed throughline 24 and valve 72 to manifold 58 for disposal or other use.

After a suitable volume of rinse water has been passed over the resinbed to reduce the amount of regenerant in the effluent, this vessel isready to be reinstalled in service, purifying water.

One of skill will recognize that there are several variations of theflows during regeneration and rinsing. For example, flows can becocurrent or countercurrent. Flows can move from vessel to vessel,displacing and pushing vessel contents.

System 400 optionally includes one or two or more additional manifolds.These manifolds are referred to as “intermediate manifolds” or “transfermanifolds”. Two such manifolds are shown as manifolds 59 and 60 whichare located in lines 74 and 76, respectively. Line 74 contains valves 78and 80 and line 76 includes valves 82 and 84. Lines 74 and 76 each spanheaders 40 and 42. These optional manifolds connect to all of thevessels and by opening and closing valves 78, 80, 82 and 84appropriately make it possible to reroute flows from one vessel toanother vessel. This rerouting through the intermediate manifolds makesit possible to achieve upflow or downflow operation in individual stepsin individual vessels if desired. It also allows parallel flows to beconverted into series flows and vice-versa These variations usingintermediate manifolds will be described in further detail withreference to the representative overall process flows depicted in FIGS.7 and 8.

Turning to FIG. 5, a second representative vessel configuration, system500, is shown. As compared to system 400, system 500 is somewhat lesscomplicated and uses somewhat fewer parts and for these reasons isgenerally preferred, particularly for processes which employ downflowpurification and cocurrent (downflow) regeneration.

System 500 has many of the features of system 400 shown in FIG. 4 whichneed not be repeated. System 500 has two intermediate manifolds 59 and60, but both are mounted on a common line 75/74/76 containing valves 78and 80 and spanning the two headers 40 and 42 on vessel 12.

System 500 is further simplified by having a manifold 52 which can beused to supply regenerant cocurrent to the water treatment flow.

Spent regenerant is taken off via manifold 54 and transferred via 3 wayvalve 86 either to regenerant storage via line 88 or to waste via line90. Regenerant can also be routed from header 42, as it leaves column12, through valve 80, through intermediate manifold 59 or 60 to a secondvessel where by opening a valve corresponding to valve 78 or valve 80the regenerant can be flowed over the resin in this second vessel incocurrent or countercurrent flow. This flow of regenerant through theintermediate manifolds and lines 74 and 75 can also be directed to theregenerant storage via line 92 and valve 94.

Rinse water, which is treated water, is available in manifold 50 and canbe fed via valve 64 upflow into header 42 and thence to column 12. Thisrinse can flow out via line 75 to manifold 59 and then to an adjacentvessel or via line 92 and valve 94 to regenerant storage as make upwater. Rinse water can also be routed for downflow feed via intermediatemanifolds 59 or 60.

As shown, the intermediate manifolds 59 and 60 can be used to rerouteflows from one vessel to another vessel. For example, regenerantsolution, particularly when only partially spent, could be passed from afirst vessel through intermediate manifold 60 or 59 to an adjacentvessel where it could pass through that second vessel's valve 78 andthence to header 40 and into that second vessel for additionalregeneration duty.

In both of the systems 400 and 500 the water flow and regenerant floware each downflow and the rinse water is either fed to the top or bottommanifold for cocurrent downflow or countercurrent upflow. While onecould, in theory, use intermediate manifold 59 or 60 to reroute theregenerant flow to countercurrent (upflow) if such flow was called for,this would not be practical for continuous operation. In this case, itwould be more sensible to connect up the feed and product lines toachieve the desired flow direction.

A representative countercurrent (upflow) regeneration system is shown inFIG. 6 as system 600. In this system regenerant is fed through manifold54 and valve 68 to lower header 42. Rinse water is available frommanifolds 50 for upflow feed as well. Effluents can be taken off vialine 44 and recycled to a second resin bed via line 75 and valve 78 viatransfer manifold 59 or 60, discharged to waste via three way valve 96and line 98 or sent to the regenerant tank via valve 96 and line 100.

In typical operation, vessels configured as shown in FIGS. 4, 5 or 6spend most of their time in service purifying water and a shorter periodbeing regenerated. The flow rate of water being treated also issubstantially greater than the rates needed for regeneration and rinse.Accordingly, the manifolds and piping for the water treatment flows canbe of larger size than the piping for regenerant and rinse flows. Thisis a particular advantage of the present invention in that theindividual vessels can be treated individually according to differenttime cycles at different steps by control of the valves feeding andremoving flows. With the prior art moving bed designs, all beds movedsimultaneously and the times for each step were locked to the bedmovement cycle.

A first embodiment of the overall system of the invention is shown inFIG. 7 as system 700. System 700 includes eighteen vessels 12-1 through12-18, where eighteen is a representative number in the range of ten totwenty-five or greater. Each vessel is numbered with an identifier “1”,“2” . . . “18” to identify its unique position in the overall system.Each vessel is configured for cocurrent flow of treatment water andregenerant essentially as set out in FIG. 5 and is equipped withheaders, manifolds, lines and valves as described with reference toFIGS. 4 and 5. These elements are numbered in accord with the numberingused in FIGS. 4 and 5 with an added indication if a particular elementis associated with a particular vessel. For example, header “40-1” isthe “40” header associated with vessel 1.

Each of the eighteen vessels contains a bed of ion exchange resin andeach has a header 40-1, etc which provides access to the vessel and tocontaminated water supplied by feed manifold 48, via valves 62-1 etc. Inthe view shown, valves 62-1 through 62-15 are shown with a black dot toindicate that arsenic-contaminated water is feeding through these valvesand through the resin beds in vessels 12-1 through 12-15. Purified wateris being withdrawn from these fifteen vessels through headers 42-1 andvalve 64-1, etc and collected in manifold 50 for use. Again, valves 64-1through 64-15 all are shown with a dot to show a positive fluid flow.

Vessels 12-16 through 12-18 are not in service removing arsenic andpurifying water. The resin beds in vessels 12-17 and 18 are undergoingregeneration with a brine solution and the bed in vessel 12-16 is beingrinsed to remove spent brine prior to being returned to service.

In a very straight forward approach, this regeneration could be carriedout by passing fresh brine from tank 102 through beds in vessels 12-17and 12-18 with the effluent going to waste via line 90. Rinse watercould be fed to vessel 12-16 from manifold 50 and this rinse water couldalso be passed to waste line 90 via intermediate manifolds 59, 54 and 60and lines 74 and 76. This would lead to large volumes of waste. This isgenerally unacceptable because the large volume of waste, however, andis not preferred. A more efficient process would minimize the volume ofwaste generated.

In a representative preferred process, vessel 12-18 is taken out ofservice filled with water. Regenerant brine that has already beenpartially used by being first passed downflow through vessel 12-17 ispassed through manifold 60 and 59 to the top of vessel 12-18 and passeddownflow through that vessel. The volume of this flow of brine isgenerally from at least about ½ a bed volume to about 3 bed volumes andespecially from about 1 to about 2 bed volumes. The first about ⅓ bedvolumes of regenerant fed to vessel 12-18 displaces the water present inthe vessel. This volume of water can be sent to product water viamanifold 50 or it can be discarded, or it can be sent to the brine tank102 via manifold 54 valve 86 and line 88. This last alternative ispreferred. The remaining regenerant passing through vessel 12-18 at thisstage can be recycled to the brine tank together with the water butpreferably up to about one bed volume of this arsenic rich brine is sentto waste via manifold 54, valve 86 and line 90.

The volume of used regenerant fed to vessel 12-18 is equal to a volumeof fresh regenerant fed to vessel 12-17 via line 53 and manifold 52.Thus, at the completion of this stage of regeneration, vessel 12-18 isfull of used regenerant and vessel 12-17 is full of fresh regenerant.

Controller 104 then reconfigures the valves associated with vessels12-16, 12-17 and 12-18 for the next stage of regeneration. In thisstage, fresh rinse water is passed from manifold 50 through valve 64-16upflow through vessel 12-16. Vessel 12-16 is full of used rinse waterpreviously added as will be described. The fresh rinse water, ½ to about1 bed volumes and preferably about ⅔ of a bed volumes, pushes used rinsewater from vessel 12-16 to manifold 52 where it passes through valves66-16 and 66-17 and flows downflow into vessel 12-17 now pushing thefresh brine previously added to 12-17 before it. This about ⅓ bedvolumes of fresh brine followed by some amount of rinse water, typicallyat least about ⅙ bed volumes to about 1 bed volumes and especially about⅓ bed volumes, are taken off via manifold 60 and passed though lines 76,valve 94 and line 92 to brine tank 102.

The fresh brine employed in the regeneration steps is most commonlycommon sodium chloride solution. This regenerant solution commonlycontains from about 2% by weight to about 15% by weight sodium chloride,especially 4 to 12% and more especially 5 to 10 and particularly about8% by weight sodium chloride.

At this stage in the regeneration process, vessel 12-16 has beencompletely rinsed and is ready to be placed in service. Vessel 12-17 isfull of partially used rinse water and vessel 12-18 is full of partiallyused regenerant brine. When the next vessel comes off line, for examplevessel 12-1, 12-16 will go into service. The regeneration cycle beginsanew with fresh brine being fed into vessel 12-18 to displace brine intovessel 12-1. Thereafter fresh rinse liquid will be added to vessel 12-17to displace its rinse liquid contents to vessel 12-18.

As can be seen, the one stage where liquid leaves the system duringregeneration is when regenerant that has passed though two vessels andis loaded with arsenic is sent to waste. In accord with this process thevolume of such liquid lost from the system is made up by the volume ofwater displaced out of the vessel when it first enters regeneration andby the volume of fresh rinse water added to the system by the finalrinse. Accordingly, the volumes of these several flows need to becoordinated to maintain a relatively constant system volume.

All of these valve and pump functions are controlled by a controller.Controller 104 opens and closes the various valves so that individualvessels can function as water purifiers or can be operated inregeneration or rinse modes. Controller 104 can operate on a preset timesequence, sequencing the various vessels through the different stationsaccording to a preset schedule. Alternatively, controller 104 canoperate based upon analytical results based on samples fed to it bysample lines 106 and associated analytical equipment which measures thecomposition of the outflows from individual vessels and cause the systemto precess from station to station based on the results of thesemeasurements. The presently preferred method of control processes thevessels based upon the volume of water passed through them and theoperator's knowledge of the capacity of the resin beds.

Controller 104 is a programmable logic controller as is marketed by AlanBradley or by Square D under the Modicon name. This computer-drivencontroller operates a program which translates a sequence of programmedcommands into a series of signals which drive the various valves andpumps in the system in an appropriate sequence to carry out the process.

System 700 is shown with all in service vessels and all vessels inregeneration operating downflow and the vessel in final rinse operatingupflow. As the various vessels cycle into these various stations theflow direction is set accordingly, not by repiping but rather bycontrolling valves and by the passing the flows through intermediatemanifolds 59 and 60, with controller 104.

System 700, with the flow directions just described, has proven veryeffective for treating water having nitrate as a principal contaminantand could work to remove arsenic but is less preferred for that servicethan system 800 which will now be described.

A second embodiment of the overall system of the invention is shown inFIG. 8 as system 800. System 800 includes sixteen vessels 12-1 through12-16. The numbering of elements of the process is in accord with thenumbering used with FIG. 7. Arsenic-contaminated water is feedingthrough the resin beds in vessels 12-1 through 12-13. Purified water isbeing withdrawn from these thirteen vessels through headers 42-1 andvalve 64-1, etc and collected in manifold 50 for use. Again, valves 64-1through 64-13 all are shown with a dot to show a positive fluid flow.

Vessels 12-14 through 12-16 are not in service removing arsenic andpurifying water. The resin beds in vessels 12-15 and 16 are undergoingregeneration with a brine solution and the bed in vessel 12-14 is beingrinsed to remove spent brine prior to being returned to service. Asnoted above, this regeneration could be carried out with substantialvolumes of regenerant and rinse going to waste but such a process wouldbe undesirable for waste disposal reasons. It should also be carried outwith substantially reduced waste, for example as follows:

In this representative preferred process, vessel 12-16 is taken out ofservice filled with water. Regenerant brine that has already beenpartially used by being first passed upflow through vessel 12-15 ispassed through manifolds 60 and 59 and lines 74 and 76 to the bottom ofvessel 12-16 and passed upflow through that vessel. The volume of thisflow of brine is generally from at least about ½ of a bed volume toabout 3 bed volumes and especially from about 1 to about 2 bed volumes.The first about ⅓ bed volumes of regenerant fed to vessel 12-16displaces the water present in the vessel. This volume of water can besent to product water or it can be discarded via line 90, or it can besent to the brine tank 102 via manifold 54, valve 79 and line 77. Thislast alternative is preferred. The remaining regenerant passing throughvessel 12-16 at this stage can be recycled to the brine tank togetherwith the water but preferably up to about one bed volume is sent towaste via manifold 54, valve 79 and line 90.

The volume of used regenerant fed to vessel 12-16 is equal to a volumeof fresh regenerant fed to vessel 12-15 via line 53 and manifold 52.Thus, at the completion of this stage of regeneration, vessel 12-16 isfull of used regenerant and vessel 12-15 is full of fresh regenerant.

Controller 104 then reconfigures the valves associated with vessels12-14, 12-15 and 12-16 for the next stage of regeneration. In thisstage, fresh rinse water is passed from manifold 50 through valve 64-14upflow through vessel 12-14. Vessel 12-14 is full of used rinse waterpreviously added as will be described. The fresh rinse water, ½ to about1 bed volumes and preferably about ⅔ of a bed volumes, pushes used rinsewater from vessel 12-14 to manifold 59 and 60 and line 76 where itpasses upflow into vessel 12-15 now pushing the fresh brine previouslyadded to 12-15 before it. This about ⅓ bed volumes of fresh brinefollowed by some amount of rinse water, typically at least about ⅙ bedvolumes to about 1 bed volumes and especially about ⅓ bed volumes, aretaken off via manifold 54 and passed though valve 79 and line 77 tobrine tank 102.

At this stage in the regeneration process, vessel 12-14 has beencompletely rinsed and is ready to be placed in service. Vessel 12-15 isfull of partially used rinse water and vessel 12-16 is full of partiallyused regenerant brine. When the next vessel comes off line, for examplevessel 12-1, 12-14 will go into service. The regeneration cycle beginsanew with fresh brine being fed into vessel 12-16 to displace brine intovessel 12-1. Thereafter fresh rinse liquid will be added to vessel 12-15to displace its rinse liquid contents to vessel 12-16, etc.

System 800, with the flow directions just described, has proven veryeffective for treating water having arsenic as its principalcontaminant. As will be described with reference to FIG. 13, the brinewaste which is produced when arsenic is the contaminant, needs to betreated to further recover the arsenic.

Turning to FIGS. 9 and 10, several details of the vessel 12 preferablyemployed in the process and system of this invention are shown. Vessel12 holds resin bed 14. Resin bed 14 substantially fills vessel 12, forexample filling at least about 85%, and preferably at least about 90%and more especially at least about 93% of the vessel volume. (In allcases these percentage fill values are based upon swollen resin in aready to use state.) Resins suitable for use in water treatment unitshave been described in the art and are selected depending upon thenature of the contaminant being removed. Table I lists a variety ofavailable resins which can be used and describes the contaminants whichthey remove.

Table I.

The ion exchange resins which are presently preferred for use in theprocess of the invention are strong base resins. These resins are basedon various polymer structures such as polystyrene with cross-linkers andwith appropriate active groups such as quaternary ammonium attached:

Prolate Strong Base Resins Type 1 and Type 2

Amberlite IRA-400

Amberlite IRA-900

Dowex SBR

Ionac ASB-1

Ionac AFP-100

Dowex SBR-P

Dowex 11

Duolite A-102-D

Ionac ASB-2

Amberlite IRA-93

Amberlite IR-45

Purolite A-400

Purolite A-600

Ionac A-260

Dowex WGR

Sybron SR6

Sybron SR7

Reillex™HPQ Resins (based on polyvinyl pyridene polymers)

Nitrex

Other ion exchange resins which are applicable to the invention such asfor treating various cations are strong acid or weak base type resinssuch as:

Amberlite IR-120

Ionac C-20

Prolate C-100

Ionac C-270

Amberlite-200

Ionac CFS

Generally, the strong base type I resins, particularly those based onpolystyrene backbones, give good overall results removing nitrate andperchlorate as well as arsenic and the like and are preferred.

Fluid flows into and out of vessel 12 are through fluid ports 108 and110, located at opposite ends of the resin bed. In preferred embodimentsof this invention, the fluid flows into and out of the vessel take placethrough fluid distributors, provided to spread the flow of liquid evenlyover the resin bed and to achieve a consistent flow of liquid over theresin bed. This provides maximum efficiency during use in service andalso during regeneration.

One approach to fluid distribution is to employ distributors such as 112and 114. These distributors may have a plurality of distributionlaterals 116, 118, 119 and 120 extending radially from a hub 122. Mostcommonly there are at least four laterals in each distributor with fromfour to eight and especially six laterals being most common. Thedistribution laterals each have a plurality of holes 124 through whichliquid can flow. These holes can be essentially evenly spaced over thelength of the laterals. It has been found that better results are oftenachieved if the holes are distributed more heavily on the outer ends ofthe distribution laterals. This tends to promote a more even andconsistent flow over the bed of resin. On the upper distributor 112 theholes 124 are concentrated toward the outer end of the laterals. On thelower distributor 114 the holes 124 are spaced along the laterals butwith the spacing between inner holes being greater than between outerholes.

Since the lower laterals may be buried in resin or may come in contactwith resin lines during downflow operation, they commonly are shieldedby a screen 126 which are closed by cap 128.

The length of the distribution laterals is typically selected to give adistributor diameter (D_(D)) which is about 66% to about 75%, andespecially about 70% of the inside diameter (D_(v)) of cylindricalvessel 12.

The flow rate of fluid through the vessels can play a part indetermining the efficiency of the system. Obviously, a very low flowrate would lead to a very low throughput for the system. Conversely, avery high flow rate could lead to inadequate treatment or inadequateregeneration or rinsing. On a commercial scale, the resin beds are fromabout two feet to about six feet in depth (length). Good results areachieved with such beds if the flow rate of liquid over the resin bed,either upflow or downflow, is from about six gallons per minute persquare foot of resin bed area (gpmft²) to about sixteen gpmft². Flowrates of eight to fourteen gpmft² and especially about twelve gpmft²give very good results particularly, when flowing contaminated waterover the resin beds for treatment. While these flow rates may usedduring each of the process steps, during regeneration and rinse it isgenerally advisable to keep the flow rates of regenerant and rinse at orabout eight gpmft².

A major process advantage of the present is the higher regenerationefficiency, as measured by smaller volumes of brine and rinse being sentto waste, which it achieves.

As illustrated in FIGS. 11 and 12, with a single fixed bed, duringregeneration, the contaminant level in the waste brine is initiallyquite high but drops rapidly as the regeneration is completed. Thismeans that the overall concentration is not optimal and that the volumeof brine is large.

As also shown in FIGS. 11 and 12 with the present invention, it ispossible to route a regenerant brine through 2, 3, 4 or more vessels inseries, varying the flow upflow and downflow as desired. This allows thebrine exiting a first vessel at the end of its regeneration cycle andthus incompletely loaded with contaminant, to pass through one or moreadditional, more contaminated, vessels and then to become fully leadedbefore being sent to waste. This multi-vessel regeneration is referredto as a “gradient regeneration”.

The brine savings produced by the system of this invention over that ofthe fixed bed system is at least 25% and often 50% or greater.

A typical regeneration/rinse cycle, using the present inventiongenerates at most about one bed volume of total waste.

When the regeneration begins, used brine first pushes ⅓ bed volumes ofwater out of the newest, most contaminated, vessel. This ⅓ bed volume ofwater is passed to the brine make up tank.

Next one bed volume of used brine is passed through that vessel. Thisone bed volume of used brine is sent to waste. This is the sole fluidsent to waste during this regeneration cycle. About ⅓ bed volumes offresh brine have been fed to the preceding vessel during this cycle butthis material only leaves the system as used brine exiting the mostcontaminated vessel.

During the rinse portion of the cycle, no waste is generated, insteadthe waste from generates ⅔ of a bed volume of spent rinse water which ispassed to the brine make up tank as make up. Thus, overall waste levelsat least as low as 0.3% are achieved during nitrate removal and as lowas about 0.01% or lower with arsenic removal.

The invention will be further described with reference to the followingExamples in which the removal of arsenic is demonstrated.

EXAMPLE 1 Arsenic Removal

The system of the invention is useful for removing arsenic from water.An overall process is illustrated in FIG. 13.

The ion exchange unit was substantially in accord with system 800 inFIGS. 8 and 13. Since this was a test system, the number of vessels wasreduced to six, three in absorption, two in regeneration and one inrinse. In a commercial scale unit, additional vessels would be presentin service in absorption for a total of at least 10 vessels. The bedswere each 36 inches in diameter and about 48 inches deep. Treated waterwas removed via line 136.

The water being treated was fed through line 130 to oxidizer 132 and hadthe following representative composition.

Anions 2.93 mg/L Ca 20.00 mg/L Cl 7.60 mg/L Mg 13.00 mg/L Mn 79.00 mg/LNO₃ 1.00 mg/L K 24.00 mg/L Na 22.00 mg/L As V 0.012 mg/L As III 0.011mg/L

This water feed was treated with chlorine (0.2 mg/L) (0.2 ppm) tooxidize the AsIII to AsV. Any equivalent oxidizer, such as 0.2 to 5 ppmchlorine or the like, can be used. It should be pointed out that thisoxidation is a very conventional step in the industry as it is common totreat water with about 0.5 ppm of chlorine during a conventional waterpurification scheme. It is not necessary to treat the water twice withchlorine.

The water feed, as treated in the oxidizer, was fed to the ion exchangeunit at a rate of 10 gpm/^(ft).

Arsenic levels were reduced to below the analytical detection limit of0.001 mg/L after 300 bed volumes of water had been fed per bed. Thislevel of performance was observed in samples taken at 3100 bed volumesand out to beyond 7500 bed volumes. At that time, beds were taken out ofservice sequentially to verify the efficacy of the regeneration steps.

The regeneration sequence described with reference to system 800depicted in FIG. 8 was used. The regenerant brine was a 7-8% by weightsodium chloride brine. The volumes and flow sequences described withFIG. 8 were used.

The flow directions were:

Absorption—downflow

First stage Regeneration—upflow

Second stage Regeneration—upflow

Rinse—upflow

The spent regenerant taken off of the first regeneration stage aseffluent to waste via line 138 contained high levels of arsenic. Thearsenic in this waste was precipitated by adding FeCl₃ solution via line142 to the effluent. 20 g FeCl₃ was added per gram of total arsenic inthe waste. The FeCl₃ converted to Fe(OH)₃ and Fe(H₂AsO₄)₃ whichprecipitated. The product, including the combined precipitate was passedvia line 144 to filter 146. The solids were recovered in filter 146 andremoved as solid toxic waste via line 148. Spent brine, with its arsenicremoved, was discharged via line 150.

This example demonstrates that arsenic can be removed continuously fromwater flows to levels below the analytical detection limit using thepresent invention's ion exchange system. The regeneration cycle is atlease 3000 bed volumes, the volume of water treated even at the scale ofthis example, with 10 to 20 columns in use can range from 1000 to 2000gpm. The liquid waste effluent can be rendered nontoxic by a simpleprecipitation process.

EXAMPLE 2 Nitrate and Arsenic Removal

This example shows the removal of nitrate and arsenic ion from a groundwater source as practiced on a continuous, pilot scale basis. Arepresentative analysis of the feed water showed the following:

Typical nitrate   50 mg/L arsenic V 0.10 mg/L arsenic III 0.10 mg/L

The product water would contain on average 6 mg/L of nitrate and lessthan 0.001 mg/L of arsenic.

The feed water is first treated with Cl₂ as described in Example 1 toconvert AsIII to AsV.

The feed water would then be fed into a purification systemsubstantially as shown in FIG. 7 as 700. Sixteen to eighteen vessels areused at various times during the run. Each vessel is 36 inches indiameter by 48 inches high. Each contains about 25 ft.³ of anionexchange resin. Commercial strong base type I an ion exchange resinhaving a DVB cross-linked polystyrene matrix and type I quaternaryammonium functional groups is used. This resin is in the form of beadswith typical resin bead size {fraction (1/16)}-{fraction (1/64)} inchdiameter. These vessels are placed in service together and removed fromservice sequentially. Eventually the vessels are cycling so that onevessel placed in service becomes loaded with contaminant, and thus inneed of regeneration about every 35-45 minutes. All 16-18 vessels areregenerated about once every 10-12 hours At most times 13 to 15 vesselsare in service with three vessels in regeneration and rinse. The nominalflow rate of the system is 1000 gpm. The vessel regeneration cycle isone recycle every 300 bed volumes of treated water. This cycle is basedupon the amount of nitrate in the feed, since this is the predominancecontaminant

Brine (8% by weight NaCl) is used as regenerant.

The flow directions used in Example 1 could be used or the followingflows could be used based on their efficiency at regenerating anitrate-loaded resin:

Absorption all downflow Regeneration all downflow (cocurrent) or laststage upflow and others downflow Rinse upflow or downflow with finalstage upflow (countercurrent)

This arrangement gives high nitrate removal efficiency and gives goodarsenic removal as well.

The regeneration cycle is as described with reference to system 700 inFIG. 7.

The first stage of regeneration, with used brine, removes arsenic andnitrate. Some of the arsenic will be removed from the column and some ofthe nitrate will be removed, leaving some nitrate at the bottom of thecolumn. The second stage of regeneration with fresh brine polishes thisbed by removing remaining traces of nitrate and arsenic.

The bed is then rinsed with water as shown in FIG. 7.

The overall efficiency of the process is very high. Nitrate will havebeen reduced to 6 mg/L arsenic is below 0.001 mg/L. The volume of wasteis 0.3%, based on the volume of purified water generated. The wastecontains about 50-60 mg/L of arsenic. This is removed by FeCl₃ addition,precipitation and filtering is set out in Example 1.

The foregoing has described the principles, preferred embodiments andmodes of operation of the present invention. However, the inventionshould not be construed as limited to the particular embodimentdiscussed. Instead, the above described embodiment should be regarded asillustrative rather than restrictive, and it should be appreciated thatvariations may be made in those embodiments by worker skilled in the artwithout departing from the scope of the present invention as defined bythe following claims.

What is claimed is:
 1. A system for continuously removing arsenic fromarsenic-contaminated water comprising: a plurality ranging from 10 to 25of immobile vessels, each containing a resin bed capable of bindingarsenic from said contaminated water and yielding purified water and aarsenic-contaminated resin bed; a plurality of electronically controlledvalves fitted to each one of the immobile vessels, one of said valvesadmitting arsenic-contaminated water to the vessel, one removingpurified water, one admitting regenerant, one admitting rinse liquid andone or more removing regenerant and/or rinse liquid; and an electricalcontroller directing the plurality of electrically controlled valves sothat when the system is in operation continuously removing arsenic,contaminated water is flowed to a subset of vessels, regenerant isflowed to a subset of vessels containing the most highlyarsenic-contaminated resin bed and rinse liquid is flowed to a subset ofvessels containing the least arsenic-contaminated resin bed.
 2. Thesystem of claim 1, wherein the electrical controller is sequenced toallow a predetermined number of vessels to be engaged in purificationwhile the others engage in regeneration while the system is inoperation.
 3. A system for continuously removing arsenic fromarsenic-contaminated water comprising: a plurality of immobile vessels,each containing a resin bed capable of binding arsenic from thecontaminated water and yielding purified water and anarsenic-contaminated resin bed, said vessels each having a first fluidcommunication opening at a first end and a second fluid communicationopening at a second end with the resin bed located there between, eachvessel having a first header directly adjacent to the first opening andconnected to the first opening and a second header directly adjacent tothe second opening and connected to the second opening, the first headerof each vessel being directly connected throughelectronically-actuatable valves to a first series of manifolds and thesecond header of each vessel being directly connected through actuatablevalves to a second series of manifolds, the first series of manifoldscomprising: (a) at least one of a manifold for supplying contaminatedwater and a manifold for removing treated water, (b) at least one of amanifold for supplying regenerant solution and a manifold for removingspent regenerant solution, and (c) at least one of a manifold forsupplying rinse water and a manifold for removing spent rinse water andthe second series of manifolds comprising the converse of the manifoldsconnected to the first headers and a controller directing the actuatablevalves (a) to flow contaminated water from a manifold over through theresin beds in a first subset of the plurality of vessels thereby causingthese resin beds to remove contaminant from said contaminated water anddeposit the contaminant upon the resin beds and yield treated water andto remove said treated water from these vessels to a second manifold,(b) to flow regenerant solution from a manifold through at least oneresin bed in a second subset of the plurality of vessels to free arsenicand regenerate said at least one resin beds, and to removearsenic-loaded arsenic spent regenerant solution from these vessels and(c) to flow rinse water from a manifold through at least one regeneratedresin bed in a third subset of the plurality of vessels to rinse said atleast one regenerated resin bed and to remove spent rinse water fromthese vessels.
 4. The system of claim 3 wherein the plurality of vesselsis at least about ten vessels.
 5. The system of claim 4 wherein thefirst subset of vessels is at least one half of the total number ofvessels.
 6. The system of claim 5 wherein the vessels additionallycomprise means for distributing fluid flows through their resin beds andwherein the vessels and the resin beds are vertically oriented with thefirst fluid openings at the top and the second fluid openings at thebottom of the resin beds.
 7. The system of claim 6 wherein the resinbeds substantially fill the vessels which contain them.
 8. The system ofclaim 5 wherein the first series of manifolds includes a firstintermediate manifold.
 9. The system of claim 8 wherein the secondseries of manifolds includes a second intermediate manifold.
 10. Thesystem of claim 9 additionally comprising a valved transfer line influid communication between the first and second intermediate manifoldsand wherein the controller controls the valve in the transfer line. 11.The system of claim 5 additionally comprising an oxidizer capable of upoxidizing the arsenic in the contaminated water.
 12. The system of claim11 additionally comprising a precipitator for precipitating arsenic fromthe arsenic-loaded spent regenerant solution.
 13. A process forcontinuously removing arsenic from arsenic-contaminated watercomprising: treating the contaminated water with oxidant to up oxidizethe arsenic contaminant, feeding contaminated water through a firstmanifold to individually-valved first headers each directly adjacent toa first opening into each of a first subset of a plurality of immobilevessels, each containing between said first opening and a second openinga resin bed capable of binding arsenic from the contaminated water andyielding treated water and an arsenic-contaminated resin bed, removingpurified water through the second opening from each of the vessels inthe first subset, and passing said treated water through a secondindividually-valved header directly adjacent to the second opening andthrough a second manifold to a treated water discharge; feedingregenerant solution to an individually-valved header directly adjacentto a first or second opening on one or more additional vessels making upa second subset of the plurality each such vessel containing anarsenic-contaminated resin bed, passing the regenerant solution over thearsenic-contaminated resin bed so that the regenerant displaces thearsenic off of the contaminated resin bed to yield a regenerated resinbed and an arsenic-loaded spent regenerant solution which is removedfrom the other opening on the vessel and through a anotherindividually-valved header directly adjacent to this opening, andtreating the arsenic-loaded spent regenerant solution to precipitate thearsenic, feeding rinse water to an individually-valved header directlyadjacent to a first or second opening on one or more additional vesselsmaking up a third subset of the plurality each such vessel containing aregenerated resin bed, passing the rinse water over the regeneratedresin bed to yield a rinsed, regenerated resin bed and used rinse waterwhich is removed from the other opening on the vessel and through theindividually-valved header directly adjacent to this opening.
 14. Theprocess of claim 13 further comprising the step of with a controller,periodically redirecting the valves to the individually-valved headersconnected to one or more of the first subset of vessels to halt the flowof contaminated and treated water to send one or more of the firstsubset of vessels and to start the flow of regenerant solution and spentregenerant solution, thereby placing said one or more vessels from thefirst subset into the second subset of vessels.
 15. The process of claim14 further comprising the step of with a controller, periodicallyredirecting the valves to the individually-valved headers connected toone or more of the second subset of vessels to halt the flow ofregenerant solution and spent regenerant solution and to start the flowof rinse water and spent rinse water, thereby placing said one or morevessels from the second subset into the third subset of vessels.
 16. Theprocess of claim 15 further comprising the step of with a controller,periodically redirecting the valves to the individually-valved headersconnected to one or more of the third subset of vessels to halt the flowof rinse water and spent rinse water and start the flow of contaminatedand treated water, thereby placing said one or more vessels from thethird subset into the first subset of vessels.
 17. The process of claim16 wherein the immobile vessels are vertically oriented with their firstopenings above the resin beds and their second openings below the resinbeds such that the flow of water is downflow through the vessels and theflows of regenerant and rinse water are upflow.
 18. The process of claim17 wherein the regenerant solution is a brine solution.
 19. A processfor continuously removing arsenic contaminant from contaminated watercomprising: a) treating the contaminated water with an oxidant to upoxidize the arsenic contaminant b) with a controller continuouslyfeeding contaminated water through a first manifold toindividually-valved first headers each directly adjacent to a firstopening into each of a first subset of a plurality of immobile vessels,each containing between said first opening and a second opening a resinbed capable of binding arsenic-contaminant from the contaminated waterand yielding treated water and a contaminated resin bed, the vessels insaid first subset having been in service for varying periods of time andthus having varying degrees of contamination of their resin beds c) witha controller continuously removing purified water through the secondopening from each of the vessels in the first subset, and passing saidtreated water through a second individually-valved header directlyadjacent to the second opening and through a second manifold to atreated water discharge, d) with a controller periodically halting thefeeding of step b) and the removing of step c) to and from the vessel inthe first subset of vessels having the most highly contaminated resinbed thereby withdrawing that vessel for purification service e) with acontroller feeding regenerant solution to an individually-valved headerdirectly adjacent to an opening on the vessel withdrawn from service instep d) and passing the regenerant solution over the contaminated resinbed so that the regenerant displaces the arsenic contaminant off of thecontaminated resin bed to yield a regenerated resin bed and anarsenic-loaded spent regenerant solution f) with a controller removingspent regenerant solution from another opening on the vessel and throughan individually-valved header directly adjacent to this opening, g) witha controller halting the feeding of step e) and the removing of step f)once a desired degree of regeneration has been attained therebywithdrawing that vessel from regeneration service, h) with a controllerfeeding rinse water solution to an individually-valved header directlyadjacent to an opening on the vessel withdrawn from service in step g)and passing the rinse water solution over the regenerated resin bed sothat the rinse water displaces regenerant solution from the regeneratedresin bed to yield a rinsed regenerated resin bed and spent rinse wateri) with a controller removing spent rinse water from another opening onthe vessel and through an individually-valved header directly adjacentto this opening j) with a controller halting the feeding of step f) andthe removing of step g) once a desired degree of rinsing has beenattained, and k) treating the arsenic-loaded spent regenerant solutionto precipitate the arsenic it contains l) reinstalling the vessel havingthe rinsed regenerated resin bed produced in step j) in service in thefirst subset of vessels.
 20. The process of claim 19 wherein at leasttwo vessels are undergoing regeneration at the same time with one ofthese vessels being more completely regenerated than another vessel andwherein fresh regenerant solution is passed over the more regeneratedresin bed and thereafter passed in series over the less completelyregenerated resin bed.
 21. The process of claim 20 wherein at least twovessels are undergoing rinsing at the same time with one of thesevessels being more completely rinsed than another vessel and whereinfresh rinse water is passed over the more rinsed resin bed andthereafter passed in series over the less completely rinsed resin bed.22. The process of claim 21 wherein the immobile vessels are verticallyoriented with their first openings above the resin beds and their secondopenings below the resin beds such that the feeding of water to thefirst subset of vessels is downflow through the resin beds.
 23. Theprocess of claim 22 wherein the flow of regenerant solution through thesecond subset of vessels is upflow.
 24. The process of claim 23 whereinthe flow of rinse water is through the third subset of vessels isupflow.
 25. The process of claim 24 wherein the regenerant solution is abrine solution.